Control systems for use with mineral mining apparatus

ABSTRACT

A hydraulic control system for controlling the shifting of roof support units and a longwall conveyor in a mineral mining installation. The units are shifted in groups by means of an automatic shifting means known per se which shifts each of the units in the associated group in succession. The control system has control devices operably associated with the first and last units of each group so that the automatic shifting sequence can commence from either the first or the last of the units. Each control device has a disc mounted in a housing and rotatable to three operating positions namely a neutral position whereat no shifting operations occur, an operating position whereat shifting of the conveyor occurs and an automatic position whereat the automatic shifting means is actuated. At each of the operating positions the disc serves to establish communication between pressure fluid boxes in the device via a non-return valve which is manually operated. The devices are interconnected by a pressure fluid conduit which serves, when pressurized, to lock the disc of one of devices when the other device is set to the automatic position and to move the disc of the one device to the neutral position. Each device also has a mechanism to ensure the disc thereof can only rotate in one direction so that it is impossible to change directly from the neutral position to the automatic position.

United States Patent [191 Weirich et al.

[4 Sept. 23, 1975 CONTROL SYSTEMS FOR USE WITH MINERAL MINING APPARATUS[75] Inventors: Walter Weirich, Dortmund; Karl Heinz Rosenhiivel,Dorfeiche, both of Germany [73] Assignee: Gewerkschaft EisenhutteWestfalia,

Westfhalia, Germany 22 Filed: Mar. 14, 1973 [21] Appl.No.: 341,012

[30] Foreign Application Priority Data Mar. 16, 1972 Germany 2212686[52] US. Cl 61/45 D; 91/427; 91/453 [51] Int. Cl. E2ld 15/44 [58] Fieldof Search 6l/45 D; 91/413, 470, 1, 91/427, 453, 170 MP [56] ReferencesCited UNITED STATES PATENTS 2,540,710 2/1951 Bush 91/427 X 2,548,1984/1951 Cosnett 91/427 X 2,940.428 6/1960 Brandstadter 91/453 X 3,207,0419/1965 Phillips 61/45 D X 3,285,015 11/1966 Carnegie et al.... 61/45 D3,319,529 5/1967 Bolton et al. 91/413 X 3,320,858 5/1967 Bolton et al.91/1 Primary Examiner-Dennis L. Taylor Attorney, Agent, or Firm-Sughrue,Rothwell, Mion, Zinn & Macpeak [57] ABSTRACT A hydraulic control systemfor controlling the shifting of roof support units and a longwallconveyor in a mineral mining installation. The units are shifted ingroups by means of an automatic shifting means known per se which shiftseach of the units in the associated group in succession. The controlsystem has control devices operably associated with the first and lastunits of each group so that the automatic shifting sequence can commencefrom either the first or the last of the units. Each control device hasa disc mounted in a housing and rotatable to three operating positionsnamely a neutral position whereat no shifting operations occur, anoperating position whereat shifting of the conveyor occurs and anautomatic position whereat the automatic shifting means is actuated. Ateach of the operating positions the disc serves to establishcommunication between pressure fluid boxes in the device via anon-return valve which is manually operated. The devices areinterconnected by a pressure fluid conduit which serves, whenpressurized, to lock the disc of one of devices when the other device isset to the automatic position and to move the disc of the one device tothe neutral position. Each device also has a mechanism to ensure thedisc thereof can only rotate in one direction so that it is impossibleto change directly from the neutral position to the automatic position.

13 Claims, 5 Drawing Figures US Patent Sept; 23,1975 Sheet 1 of 33,906,738

Hg um 1 mm Fig.4.

Fig.2.

PRIOR ART AUTOMATIC SHIFTING MEANS 2 W S A K 1 D: y R DI. P 6 T c fiall. I] M w 7 C k 5 9 R ll P US Patent Sept. 23,1975 Sheet 3 of33,906,738

CONTROL SYSTEMS FOR USE WITH MINERAL MINING APPARATUS BACKGROUND TO THEINVENTION The present invention relates to a control system forcontrolling the shifting of mineral mining apparatus which includes roofsupport units sequentially shifted with the aid of automatic shiftingmeans known per se.

In general, it is largely customary for each of the support units to beequipped with a hydraulic control valve, which is usually actuatedmanually, in order to shift the support units in succession inaccordance with the progress of the'mining work. These control valvescan be so constructed so that for each unit the removal of pressure fromthe props of the unit for their retraction the operation of feeding thesupport unit forward and the resetting of the props is accomplished byswitching over the associated control valve. Systems are already known,however, in which each support unit of the mine working is equipped withits own automatic control valve, which when initiated automaticallyperforms the entire support-shifting cycle.

It is also known to combine the support units of a mining installationinto separate operational groups, each group comprising, for example, 615 units. Each of these groups then has an automatic shifting meansassociated therewith with which all the support units belonging to thegroup in question can be automatically shifted in succession. Such ashifting means can operate hydraulically, pneumatically or electricallyand if necessary the shifting means can be designed to be actuatedremotely.

This invention is based on the known group sequence control systems, inwhich a group of support units generally comprising about 6 l andpreferably 8 12 support units of a mine working are automaticallyshifted in the preselected sequence, by selecting or switching on theautomatic shifting means associated with the group. To enable all thesupport units of the group to be shifted in this process, therefore, allthat is necessary is to initiate the control sequence, which is thencompleted automatically, and to ensure that the automatic shiftingsequence is not hindred; and proceeds safely until the last support unitof the group has been shifted.

With these points in mind a general object of the invention is toprovide an improved form of control'system for mining apparatus of theabove mentioned kind.

SUMMARY OF Tl-IE INVENTION According to the invention there is provideda control system for controlling the shifting of mining apparatus whichincludes roof support units sequentially shifted with the aid ofautomatic shifting means; said system comprising individual controldevices associated with an operational group of the support units andconnected to said shifting means so that each device is capable ofinitiating the automatic shifting sequence and interlock means forinhibiting operation of one of said devices when the other device hasinitiated said automatic shifting sequence.

In the case of a group consisting, for instance, tcn roof support unitssituated side by side along a mineral face working, the first and thetenth unit of the group can each be associated with one of the controldevices in such a way that the shifting of the entire group,accomplished by the shifting means and initiated by one of the controldevices, can start from either the first or the tenth unit as desired.The shifting of the group of units can thus be effected from either endthereof, rendering the task of the operators considerably easier andsafer and enabling the support units to be shifted more rapidly after anassociated mining machine has passed. Needless to say, it is alsopossible to use the so-called adjacent control, in which the controldevices serving to set up the automatic shifting operation are notassociated with the first and last support units of the group but onunits adjacent to these end units. In all these cases the importantrequirement is that once the automatic shifting operation has been setup by one control device it should not be possible to initiate it againby means of the other device.

In accordance with the invention this function is effected automaticallyby the interlock means when one device is actuated.

Each device preferably has an assembly which can be moved into variousoperative positions whereat in one position the automatic shiftingsequence is initiated and in another position the shifting operationsoccur. Preferably the assembly can be moved into a further positionwhereat shifting of a longwall conveyor is effected by means of pressurefluid passed through the device to the shifting rams, thereof. Theinterlocking can be effected in various ways, e.g. by mechanicallylocking the assembly of the one device in its neutral position, i.e. insaid another position, so that it cannot be moved, even by theapplication of force, into the automatic position, i.e. into said oneposition. On the other hand, the system can be so designed that theassembly of the one device is automatically returned to the neutralposition. More particularly, it is possible to arrange that theparticular control device which initiated the automatic shift sequenceis automatically returned to the neutral position by a control pulse atthe end of the automatic shifting cycle which it has initiated.

The control system of the invention is preferably constructed as a.purely hydraulic control system. The interlock means then preferablyincludes a pressure fluid conduit and a locking mechanism operablyconnected to said conduit and serving to inhibit or preventthemovementof said assembly when the conduit conveys pressure fluidthereto.

It is advisable for the control devices to be so designed that thesupport units can also be shifted by manual control independently of thesaid automatic shifting means if this proves necessary or desirable foroperational reasons. It would also be an easy matter to construct thecontrol devices in such a way that they can be actuated not onlymanually, but, if necessary, via a hydraulic, pneumatic or electricalremote control arrangement.

In a preferred form the assembly at least includes a disc mounted forrotation in a housing to effect selective communication between boresfor conveying pressure fluid and a lever connected to said disc formanually effecting said rotation to thereby adopt said operativepositions. The locking mechanism may then have a spring-loaded pistonwhich is displaced when subjected to pressure by said conduit to engagethe peripheral surface of the disc.

The disc can have a recess in its peripheral surface, said recess havingone of its defining surfaces engageable with said rod whereby the rodcan engage said surface to move the disc from the automatic position tothe neutral position.

The recess in the disc can be V-shaped and the piston may be located ina tubular structure extending tangentially to the housing for the discso that the piston rod can move the disc about its axis of rotation.

It is advisable for the control devices to each be provided with meansfor preventing the disc thereof from rotating in one direction tothereby ensure the disc cannot move directly between the neutral andautomatic positions, i.e. without the intermediary of the positionwhereat shifting of the conveyor occurs. This means may take the form ofa spring-loaded pin disposed in a bore extending radially of the disc,the inner surface of the housing surrounding the disc having recessestherein, each recess having a shoulder at one end and tapering therefromtowards the disc to the other end whereby the pin can engage on theshoulder of each of said recesses so as to allow movement of the disconly in said one direction.

The disc of each control device preferably has a central spigotcontaining a non-return valve openable by means of a plunger operated bypivotal movement of the lever. This spigot may locate in a recess of abaseplate which leads via bores to a connection on the device forreceiving pressure fluid, the disc having a sleeve offset from itscentral axis and connectible through said valve to said connection, thesleeve being selectively communicatable with further bores in thebascplate as the disc is rotated, the further bores leading to furtherconnections on the device.

The invention may be understood more readily and various other featuresof the invention may become more apparent from consideration of thefollowing description.

BRIEF DESCRIPTION OF DRAWINGS An embodiment of the invention will now bedescribed, by way of example only, with reference to the accompanyingdrawings, wherein:

FIG. 1 is a schematic diagram depicting a mineral mining installationemploying a control system made in accordance with the invention;

FIG. 1A is a schematic diagram showing the hydraulic connections betweena mineral mining installation and the control system of the presentinvention.

FIG. 2 is a plan view of a control device used in the control system;

FIG. 3 is a sectional elevational view of the device, the section beingtaken along the line III III of FIG. 2; and

FIG. 4 is a sectional plan view of the device the section being takenalong the line IV IV of FIG. 3.

DESCRIPTION OF PREFERRED EMBODIMENT Referring initially to FIG. 1, thereis shown a mineral mining installation with a conveyor F arrangedalongside a longwall mineral face K. In known manner a winning machinesuch as a plough (not shown) is guided on the conveyor F and serves tocut mineral from the face K as it is moved along the conveyor F. On thestowage side of the conveyor F remote from the face K there are aplurality of roof support units such as frames or chocks which can be ofany type. These units, depicted by rectangular boxes in FIG. 1, areshifted from time to time towards the face K, i.e. in the direction ofarrow R, as is the conveyor F also, shifting rams being provided forthis purpose. The shifting of the support units and the conveyor F iscontrolled by means of a control system made in accordance with theinvention. For this purpose the units are operably combined into groupsin generally known manner. Thus, for example one such group is composedof the units designated 1 10 in FIG. 1; the remainder of the units shownin FIG. 1 forming part of similar other groups. Each group of supportunits 1 10 has associated therewith.

a control system and automatic shifting means as shown in FIG. 1A whichmay be actuated so that when a control signal is present or a valve isoperated all the units in the group are automatically shifted insuccession. Such an automatic shifting means is known per se and is notdescribed in any detail. As is also well known in the art, each supportunit 1, 2, 9, 10 is equipped with a shifting ram R1, R2, R9, R10, and aprop P1, P2, P9, P10. Each of the rams are connected to the conveyor andare operative on being extended to advance the conveyor toward thelongwall face K, provided that the props are also in their extendedconditions, so as to wedge the units between the floor and roof.Extension of the rams is achieved by feeding pressure fluid to themalong the line Cl.

Provided that a unit is first released by retracting its prop,retraction of the ram will serve to advance the unit toward theconveyor. The prop may then be extended again to wedge the unit inposition. This sequence of operations, involving the passage of fluidthrough lines C2, C3, is controlled automatically by a shifting means M.Once the sequence has been performed and completed by unit 1, theshifting means operates to cause unit 2 to go through the .same sequenceof operation, and so on until unit 10 is in the advanced condition.

The automatic shifting means M is actuable to initiate theabove-mentioned operation by a signal along line C5. However, theprocess is bidirectional. The frame 10 can also be advanced first byactuating automatic shifting means by a signal on line C6, in which caseframe 1 is the last to move.

Thus, following advance of the conveyor caused by a signal along lineC1, an advance of the group of units, unit by unit, may be caused by asignal applied to line C5 or C6.

All of the apparatus described above, and its manner of operation, isquite conventional and well known to mining engineers.

It will be realized that the control devices S1 and S2 applying thesignals to the lines C5 and C6 must be operated in such a way as toensure that the shifting means M is not actuated by a signal in line C6,once the sequence of advancing the support units has already commencedfollowing a signal in line C5.

The subject matter of the present invention lies in the control devicesS1 and S2 shown in the lower part of FIGS. 1 and 1A.

In accordance with the invention, two control devices SI and S2 areprovided. Each receives pressure fluid through an inlet P from a mainsupply line C7, and may return fluid to a receiving tank through anoutlet PR and line C8. Three other ports are provided in each device,namely an outlet PA for connection to the line C5 or C6 as the case maybe, an outlet RL for connection to the line Cl, and an inlet 63connected to a line L which may receive fluid from the outlet PA of theother control device. The effect of a signal in the line L is to preventthe other control device from being operated when the first device isset to supply fluid from outlet PA. Accordingly, signals on both linesC5, and C6 are rendered impossible.

FIGS. 2 4 show a preferred constructional form for the control devicesS1 or S2.

Referring primarily to FIG. 3 at this stage, each of the devices S1 andS2 has a housing composed of a baseplate 20 connected with screws to ahollow pot-shaped complementary part 21. A packing ring is disposedbetween the housing part 21 and the baseplate 20. Within the housingpart 21 is a disc 22 mounted for rotation therein by means of a rollerbearing 37. The bearing 37 is accommodated in a recess in the part 21which is formed between the main wall of the part 21 and an axialshoulder projecting inwardly of the part 21. The disc 22 has a hollowspigot 23 received within a recess 24 disposed at the centre of the baseplate to guide and ensure centralization of the disc 22. The exterior ofthe spigot 23 carries a sealing ring 25 which engages the inner surfaceof the recess 24. A non-return valve is disposed within the spigot 23which is open at its outer end facing the recess 24. This valve iscomposed of a closure element in the form of a ball 27 biased by aspring 26 onto a seating 33. The seating 33 locates in a recess in themain body of the disc 22. The disc 22 also carries a hollow axial shift28 which is received within a central opening leading to the outer endface of the part 21 and partly defined by the shoulder thereof. Themating surfaces of the shaft 28 and the opening are provided withsealing or packing rings 29, 3O accommodated in grooves. The shaft 28has its hollow interior communicating with the recess in the body of thedisc 22 adjoining the interior of the spigot 23 providing a passagewaythrough these componant parts. A screw-threaded bushing 31 is receivedwithin the shaft 28 and has sealing rings provided on its outer surfacefor engagement with the interior of the shaft 28. A stepped plugdefining interior and exterior chambers joined by radial bores isdisposed between the bushing 31 and the valve seating 33. Within thebushing 31 there is disposed a displaceable plunger 32 which is guidedthrough the plug and the seating 33. The plunger 32 can be moved toengage and lift the ball 27 off the seating 33 to thereby open thenon-return valve. The wall of the central bore of the bushing 31receiving the plunger 32 also has sealing rings therein for engaging theexterior of the plunger 32. The displacement of the plunger 32 iseffected by means of a lever 34 pivotably supported on a rod 35 carriedby or connected to the shaft 28. The lever 34 has a block with a camsurface 36 which is engageable with the outer end of the plunger 32 whenthe lever 34 is pivoted in the direction of arrow Q in FIG. 3. When thelever 34 is fully pivoted in this direction the plunger 32 is maintainedin a position where the ball 27 is lifted off the seating 33 and whenthe lever 34 is returned to the position depicted in FIG. 3 the ball 27will be urged back against the seating 33 by the spring 26. The assemblyessentially composed of the components 22, 31, 34 and referred tohereinafter as the assembly can be rotated about the axis of the disc 22by means of the lever 34.

The disc 22 has a'bore 38 therein radially offset from its centre andreceiving a sleeve 40 therein. The sleeve 40, which is displaceablealong the bore 38 to a limited extent, has a sealing ring in a groove inits exterior which engages the interior of the bore 38. A flexibleabutment ring 41 is carried by the outer end of the sleeve 40 facing thebaseplate 20 so as to engage the latter. The interior of the sleeve 40and the bore 38 communicate with a bore 39 extending radially throughthe disc 22 to adjoin the exterior chamber defined by the plug disposedbetween the seating 33 and the bushing 31.

A further mounting plate 42 is connected to the baseplate 20 and packingrings are disposed between these component parts as illustrated in FIG.3. The plate 42 has an axially-directed blind bore 44 which communicateswith an extension of the recess 24 in the baseplate 20, and hence withthe valve 33, 27. The bore 44 adjoins a radially directed bore 43 in theplate 42 and the bore 43 terminates in a connection or plug P intendedfor coupling the main pressure fluid conduit C7 of the associatedpressure fluid system. The plate 42 has a further radially directed bore45 which also terminates in a connection or plug PA which is intendedfor coupling to the automatic shifting means referred to previously.This bore 45 adjoins a bore 46 extending parallel to the axis of theplate 42 and this bore 46 communicates with a similar parallel throughbore 47 in the baseplate 20 leading generally to a chamber definedexternally of the spigot 23 and at the rear faceof the disc member 22.The bore 47 is alignable with the interior of the sleeve 40 when theassembly 31, 34, 22 is rotated as described hereinafter.

The plate 42 also has a bore 48 extending parallel to its axis andleading via a radially directed conduit to a connection or plug R or PRintended for connection to a main return conduit of the pressure fluidsystem. The bore 48 aligns with a recess in the baseplate 20 containinga spring loaded plug not described in any detail leading to a returnconduit for the shifting rams.

FIGS. 1A and 2 shows particularly the various connections of the devicewith the pressure fluid system. As mentioned previously the connection Preceives pressure fluid. The connection RL serves to discharge pressurefluid to the line C1 leading to the shifting rams of the conveyor F. Theconnection PR is the main common outlet for conveying fluid to thereturn path C8 of the pressure source and the connection PA is theoutlet for conveying fluid to the automatic shifting means. The assembly34, 31, 22 can be placed into one of three rotary control positions,denoted 0, 50 and A, by means of the lever 34. The position 0 is aneutral position whereat the connectors P and RL are isolated or blockedfrom one another. The position 50 is an operating position in which theconnections P and RL communicate so that the shifting rams arepressurized to shift the conveyor F. The position A is for theinitiation of the automatic shifting means i.e. to move the units 1 10in sequence. The connectorRL leads to a bore (not shown) in thebaseplate 20 which is aligned with the sleeve 40 when the position 50 isadopted. Means in the form of a locking mechanism, describedhereinafter, ensures that the assembly 34, 31, 22 can only be rotated inthe direction of arrow T so that the assembly cannot be moved directlybetween the neutral and automatic positions and hence the automaticshifting of the units 1 10 can only take place after the shifting of theconveyor F.

This locking mechanism is depicted in FIG. 4. As shown the disc 22 has aradial bore 52 which contains a longitudinally-movable pin 51 biasedoutwardly of the bore 52 with a spring 53. The inner peripheral wall of.the housing part 21 is provided with two recessed portions 54, 55 offsetfrom one another by about 90. Each portion 54, 55 terminates at ashoulder 56 and tapers in a regular manner, in the direction of rotationT, from the shoulder 57 to merge smoothly with the main parts of theperipheral wall. The assembly 22, 31, 34 is shown in FIG. 4 in theoperating position 50 whereat the pin 51 locates on the shoulder 56 ofthe recessed portion 54 to prevent the assembly from moving other thanin the direction of arrow T. When the assembly is moved to the automaticpositions A the pin progressively retracts in the bore 52 until it canmove outwardly to engage the shoulder 56 of the recessed portion 55,thereby preventing the assembly from being moved back to the operatingposition 50.

The housing part 21 is also provided with a subhousing in the form of atubular tangential extension 58. The extension 58 has its interior 59constituting a cylinder which receives a piston 61 therein having a rodprojecting towards the disc 22. The end of the cylinder 59 remote fromthe disc 22 has a connector 63 which is intended for connection to theblocking conduit L (FIG. 1). A spring 62 is provided in the cylinder 58to bias the piston 61 outwardly away from the disc 22. When the piston61 is subjected to pressure, i.e. when the blocking conduit L ispressurized, the piston 61 will be displaced against the force of thespring 62 to force the end of the rod 60 into frictional contact withthe exterior of the disc 22. In this way the movement of the disc 28 isinhibited since a considerable amount of force would be required toeffect such movement. The device also however employs a more positivelocking facility to prevent the automatic position A from being adoptedin the presence of a pressure signal in the conduit L. This is achievedwith the aid of a V-shaped recess 64 provided in the external peripheralsurface of the disc 22. The defining surfaces 65, 66 of the recess 64extend at about 120 relative to one another. If the assembly 34, 31, 22is placed in the automatic position A the recess 64 will adopt theposition denoted 66 and assuming pressure prevails in the conduit L todisplace the piston 61 as discussed above the rod 60 will engage thesurface 66 to urge the disc 22 in the direction of arrow T. Hence theassembly cannot adopt the automatic position A when a pressure signal ispresent in the conduit L.

The operation of the control system employing the devices S is asfollows:

Assuming that the group of support units 1 (FIG. 1) are stabilized inthe roof support position, the devices S1 and S2 will be set in theneutral position 0, in which the connection P is blocked from theshifting rams of the conveyor F. The conduit L is not subjected topressure, so that the assembly 22, 31, 34 of each device S1 and S2 isfree to rotate. After the mining machine has moved past the group 1 10the next operation is to shift the conveyor F. This is effected bymoving the lever 34 of one device S1 or 52 into the operating position50 and pivoting the lever 34 to open the valve 33, 27. The controldevice in question now allows hydraulic pressure fluid to be supplied tothe shifting rams of the conveyor F. The fluid flows from the connectionP through the bores 43 and 44 and the opened valve 33, 27 through theradial bore 39 and into the sleeve 40. From here the fluid flows intothe bore (not shown) in the baseplate leading via the connector RL tothe shifting rams of the conveyor F. The shifting rams now displace theconveyor F over the section situated in front of the group 1 10 towardsthe face K in the direction shown by the arrow R in FIG. 1. After theconveyor F is moved the group of units 1 10 can likewise be shifted.This is achieved by partially rotating the assembly 31, 22 34 of controldevice S1 into the automatic position A and again pivoting the lever 34to open the valve 33, 27. In this latter position pressure fluid fromthe connection P flows through the bores 43, 44, the opened valve 27, 33and the bore 39 into the sleeve 40. From here the fluid passes into thebore 47 and thence through the bores 46, 45 to the connection PA leadingto automatic shifting means which once ac- I tuated automatically shiftsthe entire group of units 1 10, starting with the first support unit 1and terminating with the last support unit 10.

It is assumed that the shifting means is such that the shiftingoperation commences with the support unit 1 and terminates with thesupport unit 10. It is also possible, however, to arrange for the unitsto be shifted in the reversed order, i.e. starting with the support unit10 and terminating with the support unit 1.

In order to ensure that during the shifting of the group 1 10 the otherdevice S2 cannot be operated the latter is locked when the assembly 31,34, 22 of the first device S1 is turned into the automatic position A.This is essentially achieved by the conduit L which is connected to theconnection PA of the first device S1. Then as described before, the rod60 of the other device S2 locks the assembly 31, 34, 22 thereof. Asecond line L, now shown, is of course provided from the connection PAof the control device S2 to the connection 63 of the device S1 for whenoperation proceeds in reverse order, starting with frame 10 first.

After the shifting of the group 1 10 the assembly 31, 34, 22 of thedevice S1 or S2 by which the shifting of the group 1 10 was originallyinitiated, remains in the automatic position A. Further shifting of thegroup 1 10 by means of this device S1 or S2 can then only be carried outif the assembly 31, 34, 22 of this device S1 or S2 is moved from theautomatic position A in the direction shown by the arrow T in FIG. 4 viathe 0 position and the operating position 50, back to the automaticposition A to re-initiate the automatic-shifting means. Further shiftingof the group 1 10 can also be set up by actuating the other device S1 orS2, in which case the device S1 or S2 which was actuated first beforeand which is still in the automatic position, is automatically movedfrom the latter position by means of the rod 60 engaging the surface 66as described before.

The system could also be arranged and constructed however, in such a waythat after the completed shifting of the group 1 10 the device S1 or S2which was moved to the automatic position A to initiate the shifting, isautomatically returned to its neutral position 0. In this case, as soonas the shifting process is terminated the assemblies 31, 34, 22 of bothdevices S are released and operable.

We claim:

1. In a hydraulically operable mine roof support arrangement, whichcomprises a group of roof support units and an automatic shifting meansfor controlling the advance of the units in an ordered sequence from oneor other end of the group, depending upon which of two input lines tothe shifting means is pressurized, the improvement comprising a controlsystem for initiating the operation of the shifting means, said controlsystem comprising two devices each of which is adapted to supplypressure fluid to a respective one of the two input lines to theshifting means, each device being adapted to be placed in a condition inwhich pressure fluid may be supplied through the device to the inputline and interlock means operable upon one of said devices being placedin the condition aforesaid to prevent the other device being placed insaid condition or to reset the said other device in a neutral condition.

2. A system according to claim 1, wherein each device has an assemblywhich can be moved into various operative positions whereat in oneposition pressure fluid is supplied to the automatic shifting means andin another position no fluid is so supplied.

3. A system according to claim 2, wherein said assembly can be movedinto a further position whereat shifting of a longwall conveyor iseffected.

4. A system according to claim 2, wherein said interlock means has apressure fluid conduit connected between said devices and a lockingmechanism for each device which at least inhibits movement of theassembly thereof when the pressure fluid conduit is pressurized.

5. A system according to claim 4, wherein the locking mechanism has aspring-loaded piston which is displaced when subjected to pressure bysaid conduit to engage the assembly.

6. A system according to claim 2, wherein said assembly at leastincludes a disc mounted for rotation in a housing to effect selectivecommunication between bores for conveying pressure fluid and a leverconnected to said disc for manually effecting said rotation to therebyadopt said operative positions.

7. A system according to claim 5, wherein the assembly at least includesa disc mounted for rotation in a housing to effect selectivecommunication between bores for conveying pressure fluid and a leverconnected to said disc for manually effecting said rotation to therebyadopt said operative positions and wherein the housing has a tubularextension receiving said piston and extending substantially tangentiallyto the peripheral surface of the disc so that the rod is directlyengageable with the peripheral surface of the disc.

8. A system according to claim 6, wherein the disc carries a non-returnvalve having a spring-loaded closure element movable to open the valvewith the aid of a plunger, the plunger being connected to said lever sothat pivotal movement of the lever effects opening of the valve.

9. A system according to claim 8, wherein the valve is contained in aspigot provided at the centre of the disc and locating in a recess in abaseplate which leads via bores to a connection on the device forreceiving pressure fluid, the disc having a sleeve offset from itscentral axis and connectible through said valve to said connection, thesleeve being selectively communicatable with further bores in thebaseplate as the disc is rotated, the further bores leading to furtherconnections on the device.

10. A system according to claim 7, wherein the disc has a recess in itsperipheral surface; said recess having one of its defining surfacesengageable with said rod whereby the rod can move the disc away fromsaid one position to said another position when the conduit conveyspressure fluid to said piston.

11. A system according to claim 2, wherein there is provided means forpreventing rotation of the disc in one direction to ensure that the disccannot be moved directly from said another position to said oneposition.

12. A system according to claim 1 1, wherein the preventing means is inthe form of a spring-loaded pin disposed in a bore extending radially ofthe disc, the inner surface of the housing surrounding the disc havingrecesses therein, each recess having a shoulder at one end and taperingtherefrom towards the disc to the other end whereby the pin can engageon the shoulder of each of said recesses so as to allow movement of thedisc only in said one direction.

13. A mine roof support control system, comprising two control devices,each said device having first, second, third and fourth ports, saidfirst port being connected to a main hydraulic supply conduit, saidsecond port being connected to a conduit to mine roof support shiftingrams, said third port being connected to an automatic shifting means andthe fourth port being connected to the third port of the said otherdevice, operating means movable to a first position to connect saidfirst port to said second port, and to a second position to connect saidfirst port to said third port, and interlock means responsive topressure applied at said fourth port to prevent movement of saidoperating means to said second position.

1. In a hydraulically operable mine roof support arrangement, whichcomprises a group of roof support units and an automatic shifting meansfor controlling the advance of the units in an ordered sequence from oneor other end of the group, depending upon which of two input lines tothe shifting means is pressurized, the improvement comprising a controlsystem for initiating the operation of the shifting means, said controlsystem comprising two devices each of which is adapted to supplypressure fluid to a respective one of the two input lines to theshifting means, each device being adapted to be placed in a condition inwhich pressure fluid may be supplied through the device to the inputline and interlock means operable upon one of said devices being placedin the condition aforesaid to prevent the other device being placed insaid condition or to reset the said other device in a neutral condition.2. A system according to claim 1, wherein each device has an assemblywhich can be moved into various operative positions whereat in oneposition pressure fluid is supplied to the automatic shifting means andin another position no fluid is so supplied.
 3. A system according toclaim 2, wherein said assembly can be moved into a further positionwhereat shifting of a longwall conveyor is effected.
 4. A systemaccording to claim 2, wherein said interlock means has a pressure fluidconduit connected between said devices and a locking mechanism for eachdevice which at least inhibits movement of the assembly thereof when thepressure fluid conduit is pressurized.
 5. A system according to claim 4,wherein the locking mechanism has a spring-loaded piston which isdisplaced when subjected to pressure by said conduit to engage theassembly.
 6. A system according to claim 2, wherein said assembly atleast includes a disc mounted for rotation in a housing to effectselective communication between bores for conveying pressure fluid and alever connected to said disc for manually effecting said rotation tothereby adopt said operative positions.
 7. A system according to claim5, wherein the assembly at least includes a disc mounted for rotation ina housing to effect selective communication between bores for conveyingpressure fluid and a lever connected to said disc for manually effectingsaid rotation to thereby adopt said operative positions and wherein thehousing has a tubular extension receiving said piston and extendingsubstantially tangentially to the peripheral surface of the disc so thatthe rod is directly engageable with the peripheral surface of the disc.8. A system according to claim 6, wherein the disc carries a non-returnvalve having a spring-loaded closure element movable to open the valvewith the aid of a plunger, the plunger being connected to said lever sothat pivotal movement of the lever effects opening of the valve.
 9. Asystem according to claim 8, wherein the valve is contained in a spigotprovided at the centre of the disc and locating in a recess in abaseplate which leads via bores to a connection on the device forreceiving pressure fluid, the disc having a sleeve offset from itscentral axis and connectible through said valve to said connection, thesleeve being selectively communicatable with further bores in thebaseplate as the disc is rotated, the further bores leading to furtherconnections on the device.
 10. A system according to claim 7, whereinthe disc has a recess in its peripheral surface; said recess having oneof its defining surfaces engageable with said rod whereby the rod canmove the disc away from said one position to said another position whenthe conduit conveys pressure fluid to said piston.
 11. A systemaccording to claim 2, wherein there is provided means for preventingrotation of the disc in one direction to ensure that the disc cannot bemoved directly from said another position to said one position.
 12. Asystem according to claim 11, wherein the preventing means is in theform of a spring-loaded pin disposed in a bore extending radially of thedisc, the inner surface of the housing surrounding the disc havingrecesses therein, each recess having a shoulder at one end and taperingtherefrom towards the disc to the other end whereby the pin can engageon the shoulder of each of said recesses so as to allow movement of thedisc only in said one direction.
 13. A mine roof support control system,comprising two control devices, each said device having first, second,third and fourth ports, said first port being connected to a mainhydraulic supply conduit, said second port being connected to a conduitto mine roof support shifting rams, said third port being connected toan automatic shifting means and the fourth port being connected to thethird port of the said other device, operating means movable to a firstposition to connect said first port to said second port, and to a secondposition to connect said first port to said third port, and interlockmeans responsive to pressure applied at said fourth port to preventmovement of said operating means to said second position.